Multiple spindle automatic bar machines generally employ collet chucks for holding end working tools such as drills, spot drills, center drills, counterbores, spot facers, combination drills and countersinks, reamers, end mills, and hollow mills, the integral shanks of the chucks being longitudinally adjustably clamped in the end working tool slides (or auxiliary slides thereon) which are moved toward and away from the spindle carrier. The use of end working tool chucks of the character indicated adds substantially to set-up time in that it entails longitudinal adjustment of the tools in the respective chucks and of the chucks in the end working tool slides with respect to the spindle drum face of the machine. Moreover, replacement of dull or broken tools entails substantial down time of the machine whether the tools are replaced at the machine or in the chucks removed from the machine.